2 files changed, 60 insertions, 0 deletions
diff --git a/src/fields/KeyStore.ts b/src/fields/KeyStore.ts
index 9c7a45af4..68883d6f1 100644
--- a/src/fields/KeyStore.ts
+++ b/src/fields/KeyStore.ts
@@ -37,6 +37,7 @@ export namespace KeyStore {
     export const CurPage = new Key("CurPage");
     export const NumPages = new Key("NumPages");
     export const Ink = new Key("Ink");
+    export const Cursors = new Key("Cursors");
     export const OptionalRightCollection = new Key("OptionalRightCollection");
     export const Archives = new Key("Archives");
     export const Updated = new Key("Updated");
diff --git a/src/fields/TupleField.ts b/src/fields/TupleField.ts
new file mode 100644
index 000000000..e2162c751
--- /dev/null
+++ b/src/fields/TupleField.ts
@@ -0,0 +1,59 @@
+import { action, IArrayChange, IArraySplice, IObservableArray, observe, observable, Lambda } from "mobx";
+import { Server } from "../client/Server";
+import { UndoManager } from "../client/util/UndoManager";
+import { Types } from "../server/Message";
+import { BasicField } from "./BasicField";
+import { Field, FieldId } from "./Field";
+
+export class TupleField<T, U> extends BasicField<[T, U]> {
+    constructor(data: [T, U], id?: FieldId, save: boolean = true) {
+        super(data, save, id);
+        if (save) {
+            Server.UpdateField(this);
+        }
+        this.observeTuple();
+    }
+
+    private observeDisposer: Lambda | undefined;
+    private observeTuple(): void {
+        this.observeDisposer = observe(this.Data as (T | U)[] as IObservableArray<T | U>, (change: IArrayChange<T | U> | IArraySplice<T | U>) => {
+            if (change.type === "update") {
+                UndoManager.AddEvent({
+                    undo: () => this.Data[change.index] = change.oldValue,
+                    redo: () => this.Data[change.index] = change.newValue
+                })
+                Server.UpdateField(this);
+            } else {
+                throw new Error("Why are you messing with the length of a tuple, huh?");
+            }
+        });
+    }
+
+    protected setData(value: [T, U]) {
+        if (this.observeDisposer) {
+            this.observeDisposer()
+        }
+        this.data = observable(value) as (T | U)[] as [T, U];
+        this.observeTuple();
+    }
+
+    UpdateFromServer(values: [T, U]) {
+        this.setData(values);
+    }
+
+    ToScriptString(): string {
+        return `new TupleField([${this.Data[0], this.Data[1]}])`;
+    }
+
+    Copy(): Field {
+        return new TupleField<T, U>(this.Data);
+    }
+
+    ToJson(): { type: Types, data: [T, U], _id: string } {
+        return {
+            type: Types.Tuple,
+            data: this.Data,
+            _id: this.Id
+        }
+    }
+}
+\ No newline at end of file